nwfilter: clear nrules when resetting virNWFilterInst

It's possible/probable the callers to virNWFilterInstReset() make it
unnecessary to set the object's nrules to 0 after freeing all its
rules, but that same function is setting nfilters to 0, so let's do
the same for the sake of consistency.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/nwfilter/nwfilter_gentech_driver.c

@@ -240,6 +240,7 @@ virNWFilterInstReset(virNWFilterInstPtr inst)
     for (i = 0; i < inst->nrules; i++)
         virNWFilterRuleInstFree(inst->rules[i]);
     VIR_FREE(inst->rules);
+    inst->nrules = 0;
 }